Some cells are uncontrolled in the sense that a PLMN (public land mobile network) operator does not control the location and/or operation of the cell. Other cells are controlled in the sense that the operator does control both the location and operation of the cells. Examples of uncontrolled cells include, for example, CSG (closed subscriber group) cells, cells controlled by home enode b's and home node b's. These cells are also sometimes referred to as being “uncoordinated” in the sense that they are not subject to normal radio/cell planning.
It is generally understood that there are many methods of performing a handover for controlled cells. Inbound handover in this context refers to a cell change from a target cell's perspective where resources (for example timeslots, frequency channels, scrambling codes, etc.) for transmission and/or reception in the cell are allocated to a mobile station in advance of the mobile station performing a cell change to that cell, particularly in response to a request from the controller of the device's serving cell.
While the uncontrolled cells may be configured to use spectrum that is owned by the operator, the network operator does not have the same control over uncontrolled cells as for controlled cells. Typically, the network operator does not own the support structure (towers etc.), does not own or control the backhaul connection (e.g. Digital Subscriber Line (DSL) connections), does not know or control when a given uncontrolled cell is going to be switched on, and may not know or control the locations of uncontrolled cells. The operator will typically still have control of various parameters such as operating frequency, transmit power, etc. if the operator owns the spectrum license.
In order to perform a handover to a target cell, controlled or uncontrolled, a MS (mobile station) typically needs to provide identifying information relating to the target cell to the current serving cell so that it can initiate a handover process. In particular, the current serving cell needs to be able to communicate with (possibly via a core network) the cell controller for the target cell. However, the current serving cell may not be aware of how to reach the cell controller for the target cell, particularly if the target cell is an uncontrolled cell, unless provided with explicit identification information for the cell (such as a cell global identity). This makes handover to such cells difficult. In contrast, for a controlled target cell, it may be sufficient for the mobile station to provide the current serving cell with information about the target cell. This does not require or cause the acquisition of any broadcast information from the target controlled cell for the serving cell to be able to reach the cell controller for the target controlled cell, since the serving cell or some part of the network may be able to map other identifying features of the cell (such as operating frequency, scrambling code etc.) to the identity of the target cell or its controller.
There are three modes of operation relating to mobility from a GERAN (GSM EDGE (Enhanced Data rates for GSM Evolution) Radio Access Network) cell to another (not necessarily GERAN) cell. The commanded mode is indicated in broadcast signalling (NETWORK_CONTROL_ORDER sent in SI2quater message, see 3GPP TS 44.018), but may also be signalled in point-to-point signalling. The commanded mode applies both in packet transfer mode and in packet idle mode. If a circuit-switched connection is active (e.g. in a voice call), different procedures apply (approximately similar to the rules for NC2 described below, although handover is the only permitted means of cell change in this case). The three modes are:                NC0: In this mode, cell reselection is autonomous (i.e. is performed by the mobile without being prompted by the network). Criteria for reselection are specified and parameters relating to these criteria may be transmitted by the network;        NC2: In this mode, the mobile sends measurement reports to the network indicating the signal strength/quality of neighbouring cells; based on these reports, the network directs the mobile to perform cell reselection or handover. Autonomous reselection in this mode is not permitted; and        NC1: This is a hybrid of NC0 and NC2; in this mode, the mobile station performs autonomous reselection if the appropriate criteria are met. However, the mobile station also transmits measurement reports to the network, allowing the network to trigger reselection/handover as in NC2 mode.        
The network may indicate that a CCN (Cell Change Notification) procedure should be performed by a particular mobile station, or mobile stations generally, in respect of certain neighbour cells or neighbour cells using a certain radio access technology (RAT). Typically the network indicates that the Cell Change Notification procedure is to be performed through broadcast system information. However, it may also be signalled using point-to-point signalling (e.g. in a Packet Measurement Order (PMO) message). The existing fields to indicate this include:                CCN_ACTIVE (sent in GPRS (General Packet Radio Service) Cell Options, see 3GPP TS 44.060, applicable to GSM (Global System for Mobile Communications) cells),        CCN_SUPPORTED (sent in System Information (SI) type 2quater (SI2quater) see 3GPP TS 44.018, applicable to individual GSM target cells),        3G_CCN_ACTIVE, E-UTRAN_CCN_ACTIVE (sent in SI2quater, applicable to 3G (Third Generation, such as UMTS (Universal Mobile Telecommunications System)) and E-UTRAN (Evolved Universal Terrestrial Radio Access Network) cells respectively; these indications apply on a per-RAT basis, i.e. to all target cells of that radio access technology).        
With current definitions, CCN is applicable only when the mobile station is in packet transfer mode and in either NC0 or NC1 mode.
If, for the target cell for which reselection criteria are met, CCN is active or enabled, then the mobile station sends a Packet Cell Change Notification (PCCN) message to the network identifying the selected target cell before performing reselection.
Upon receiving a PCCN, the network may:
a) do nothing: after timers elapse at the mobile station, the mobile station will continue with reselection;
b) order the mobile station to continue reselection to the selected cell, by sending a Packet Cell Change Continue (PCCC) message; a Packet Cell Change Order (PCCO) message may also be used in this case;
c) order the mobile station to perform reselection to a different cell by sending a Packet Cell Change Order (PCCO) message;
d) initiate a packet-switched handover procedure; this involves a preparation phase in which the target cell receives advance notification of the mobile station's intended cell change, the target cell reserves resources and informs the mobile, via the serving cell, of these resources. This approach can reduce the service interruption time associated with cell change.
Before sending a PCCO or PCCC indicating a cell change to a GERAN cell, the network may send neighbour cell system information to the mobile station. This may include some or all of the system information that the mobile station would otherwise need to receive in the target cell before establishing packet transfer mode. One of the benefits of the CCN procedure is to allow the mobile station to receive this information before performing reselection and hence to avoid needing to receive it in the target cell, which may cause service interruption.
Before sending a packet-switched handover command where the target cell is a GSM cell, the network sends the neighbour cell system information.